In oil and gas wells, it is common to conduct well testing and stimulation operations to determine production potential and enhance that potential. Annulus pressure responsive downhole tools have been developed which operate responsive to pressure changes in the annulus between the testing string and the well bore casing and ran sample formation fluids for testing or circulating fluids therethrough. These tools typically incorporate both a valve ball and lateral circulation ports. Both the valve ball and circulation ports are operable between open and closed positions.
A tool of this type is described in U.S. Pat. No. 4,633,952 issued to Ringgenberg and assigned to Halliburton Company. A commercially available multi-mode testing tool of this type is the "Omni SandGuard IV Circulating Valve." The tool is capable of performing in different modes of operation as a drill pipe tester valve, a circulation valve and a formation tester valve, as well as providing its operator with the ability to displace fluids in the pipe string above the tool with nitrogen or another gas prior to testing or retesting. A popular method of employing the circulating valve is to dispose it within a well bore and maintain it in a well test position during flow periods with the valve ball open and the circulation ports closed. At the conclusion of the flow periods, the tool is moved to a circulating position with the ports open and the valve closed. The tool is operated by a ball and slot type ratchet mechanism which provides opening and closing of the valve responsive to a series of annulus pressure increases and decreases.
Unfortunately, the changing between tool modes in the type of tool described in U.S. Pat. No. 4,633,952 is limited in that the ratchet dictates preprogrammed steps for changing the tool between its different positions. An operator must follow each of the preprogrammed steps to move the tool between positions. A standard circulating valve ratchet, for instance, requires 15 cycles of pressurization and depressurization in the annulus to move the tool out of the well test position, into the circulating position and back again. This process requires approximately one hour.
It is desirable, therefore, to employ a tool which allows an operator to shift the tool from a well test position to a circulating position with a minimum of pressure cycles. An operator would be able to maintain his tool in the well test position and close the tool when desired without following a preprogrammed cycle schedule. The number and times of closures could be orchestrated in accordance with programs established by reservoir engineers or supervisors.
A tool of this type is described in U.S. Pat. No. 5,482,119 issued to Kevin R. Manke and Curtis Wendler and assigned to Halliburton Company, entitled "Multi-Mode Well Tool With Hydraulic Bypass Assembly. The specification of U.S. Pat. No. 5,482,119 is hereby incorporated by reference in its entirety. This annulus pressure responsive tool contains lateral circulation ports and a valve ball, each of which are operable between open and closed positions to configure the tool into different modes of operation. These modes include a well test position in which the valve ball is open and the circulation ports are closed, a blank position in which the valve ball and circulation ports are both closed, and a circulating position in which the valve ball is closed and the circulation ports are open. Through manipulation of annulus pressure, the tool mode can be changed upon reduction or release of annulus pressure to move the tool out of the well test position and into the blank and circulating positions.
The type of tool described in U.S. Pat. No. 5,482,119 includes an operating mandrel assembly that is slidably disposed within the exterior housing of the tool whose movement dictates the positions of both the circulation ports and the valve ball. The operating mandrel is moveable by means of an annulus pressure conducting channel which is capable of receiving, storing and releasing annulus pressure increases.
A ratchet assembly associates the operating mandrel assembly and housing and functions as an overrideable position controller which dictates response and movement of the operating mandrel assembly to annulus pressure changes. The ratchet assembly contains a pair of ratchet balls which travel in ratchet slots on a ratchet slot sleeve. The ratchet slots feature a well test travel path within which the ratchet balls are maintained during normal operation of the tool in its well test position. A secondary ratchet path is contiguous to the well test path. The ratchet balls may be redirected into the secondary ratchet path and moved to ratchet ball positions which permit the operating mandrel assembly to be moved to positions corresponding to blank and circulating modes for the tool.
A fluid metering assembly includes upward and downward fluid paths for flow during annular pressure changes. The upward flow path toward the fluid spring during annulus pressurization permits relatively unrestricted fluid flow. The downward flow path away from the fluid spring during a release of annulus pressure provides metered flow to provide an operator sufficient time to generate an annulus pressure increase to move the rachet balls out of the well test travel path and into the secondary path.
A hydraulic bypass assembly is included which selectively reduces the time required for portions of the metered transmission of stored fluid pressure away from the fluid spring. The bypass assembly includes a bypass mandrel and associated fluid communication bypass grooves which increase the flow of fluid away from the fluid spring and toward the rachet assembly during portions of the pressure release operation.
Nevertheless, a tool of the type disclosed in U.S. Pat. No. 5,482,119, while more flexible and faster in operation than earlier designs, still depends on a precision combination of time and pressure to control the positions of the tool. This design requires timed cycles of pressure up and bleed-off. It would be desirable, therefore, to employ an improved tool which will allow an operator to shift the tool from a well test position to a circulating position based on the principle of pressure alone. This would result is substantially simplified operation and improve the ability to control the modes of the tool. In addition, the operation time would be further reduced if the metering mechanism could be eliminated.